Process of finishing leathers and product



Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE- DUCT James T. Power, Wilmington, Del.,

Atlas Powder Company, 'W'

assignor to 11, Del., a

corporation of Delaware No Drawing. Application January 31, 1935, sci-mm. 4.30s. Renewed May 14, 19:6

20 Claims.

This invention relates to the finishing of leathers and particularly to the finishing of soft or light leathers. The invention has for its object to improve the finish of leathers; These improvements consist of (1) the production of a softer and more flexible finished leather than is obtained with present known materials or methods; (2) a reduced susceptibility to changes in the properties of leathers with changes in humidity conditions. Further objects and advantages will be set forth in the following description and in the claims appended thereto.

The animalskins from which leather is made consist of a natural fabric of interwoven fibers. The leather tanner cannot alter the fabric structure to any appreciable extent, and so his problem is the treatment and finishing of the fiber structure given him, so as to produce the desired texture. The skin must first be freed from dirt and blood and other adventitious material, and the hair, epidermis and flesh removed. Then the skin must be so treated as to reduce its sensitiveness to water and render'it resistant to putrefaction. This in turn must be followed. by a. series of finishing operations designed to give the skin the proper mechanical feel, surface appearance and waterproof or water-resisting characteristics.

The types of tanning and finishing operations obviously depend on the final use of the leather,

'e. g. heavy leather for sole leather, etc., and

light or soft leather for shoes, gloves and the like. Thus the various steps in preparing a glac kid. leather, for example, would probably include soaking, painting, liming'and deliming,

puering, pickling, chrome tanning, washing and neutralizing, dyeing, fatliquoring, damping and staking, oiling off or clearing and seasoning, glazing and the final finishing. These steps may be modified in a number of ways by those skilled in the art in order to produce various effects or finishes. For example, an enzyme treatment may be substituted for or used in addition to the steps of painting, liming and deliming.

This invention is mainly concerned with the treatment of the skin following its conversion to leather by the tanning operation. For example, with a chrome tanned leather, if it be dried out, it will be converted into horn by the adhesion of the fibers of the mass due to the plasticity of their surfaces, and it cannot be wet back to its former soft hydrated state. It is therefore imperative to fatliquor tanned leather after tanning and before drying out, so as to prevent the coalescence of the fibers on dehydra tion. Once thus properly dried, the fibers have lost their plasticity and the leather can be wet back indefinitely without adhesion of the fibers.

It has'been the practice to fattenwith glycerine mixed with vegetable or other oils; glycerine, and soaps of these oils; glycerine and sulphonated oils; egg yolk and oils; or egg yolk alone. Various combinations of the above are sometimes used depending upon the particular hides undergoing treatment and the finish desired. Glycerine when thus used depends in part for its effect upon its hygroscopic and softening nature which causes the retention of moisture in the fabric; thus enhancing the fullness and softening effect. Glycerine as a finishing agent is at a disadvantage because of its extreme avidity for moisture under conditions of high humidity. Leathers treated with glycerine as a finishing agent when exposed to high humidity show a large increase in surface area, which is a disadvantage; for example, in themanufacture: of leather for use in making shoes and similar articles where increase in surface area should be at a minimum under conditions of high humidity. Leathers containing any considerable amount of glycerine absorb so much moisture when exposed to conditions of high humidity that they become limp. exhibiting what is known to the art as a raggy" efiect. Consequently the tanners or finishers of leather cannot take full advantage of the softening effect of glycerine, being forced to keep the glycerine concentration in the finishing operations low enough to avoid the difllculty mentioned above. g 1' Now I have found that some of the hexahydric alcohols as well-as many water soluble derivativesof hexahydric alcohols offer distinctadvantages as ingredients in the finishing process. An example of a hexahydric alcohol which is suitable for use in the finishing process is sorbitol. In the finishing process with equal'concentrations, sorbitol produces a greater. softening effect upon leathers than does glycerine. S017 bite] is a hygroscopic substance, but I find that while sorbitol absorbs approximately the same amount of moisture from atmospheres 0f low humidities as does 'glycerine, at high relative humidities it absorbs much less moisture than does glycerine. The increasein area of leather finished with sorbitol when exposed to high humidity conditions is much lessthan in the case of leathers treated with glycerine.

The amounts .of moisture absorbed by glycerine and sorbitol when allowed to come to equilibrium 6 with atmospheres of various relative humidities are shown in the following table:

Weight of moisture absorbed by 100 g. of Relative humidity l Glycerinc Sorbitol Percent Another hexahydric alcohol which is hygroscopic and may be used in place of glycerine in finishing leather is iditol.

Among the water soluble hygroscopic derivatives of hexahydric alcohols I may mentioned monoanhydro sorbitol or sorbitan, dianhydro sorbitol or sorbide, monoanhydro mannitol or mannitan, dianhydro mannitol or mannide, monoanhydro dulcitol or dulcitan and dianhydro dulcitol or dulclde.

The leather treated with these compounds will show smaller variations in moisture content, when subjected to varying humidity conditions, than will the same leather treated withglycerine. Thus the finisher can take full advantage of the superior softening action of sorbitol, for example; without fear of the development. oi. ragginess and possible stretching should the be exposed to atmospheres of high humidity.

, Moreover, I have found that a leather treated,

with a hygroscopic hexahydric alcohol, or a water soluble hygroscopic anhydro derivative of a hexa-.

hydric alcohol at the proper stage of the finishing operation, has a superior body" to that of a similar leather treated with a like concentration of glycerine.

In the following examples I have chosen as the preferred embodiment of my invention the hexahydric alcohol sorbitol. However, it is to be understood that'proper amounts or iditol, sorbitan,

sorbide, etc., may be substituted for the sorbitol if so desired.

The following example represents one recipe for fat liquor to follow the tanning operation:

I. Castor oil soap lbs 3 Sorbitol lbs 2- Castor oil. lbs 1% Boiling water lbs (10 Other vegetable oils, sulphonated oils, animal and marine oils may oil, as for example:

11; SOIl'bit l 1h 1 Castile soap lbs 1% Neats-foot oil lbs 2 Borax oz 4 Water lbs 150 Another example oi. a fat liquor suitable for treating the leather after tanning is as follows:

III. Degras lbs 10 Olive oil lbs 10 Sorbitol lbs 4 Soft soap lbs 5 Water at '140 F gals -70 The skins are tumbled in this emulsion for a period in the neighborhood of 45 minutes and are then hung on a trestle for about 30 minutes to let the fat penetrate the leather.

However, the sorbitol treatment may occur in the oiling oi! operation, in which case it may or leather be used in place of castor IV. Sorbitol syrup of 85% sorbitol content lb 1 Water lbs 3 I have found that a superior result was obtained with this sorbitol recipe in comparison with a mixture of 1 part of C. P. glycerine and 1 part water. The sorbitol mixture given in Example IV can be applied by spreading the tanned colored and fat liquored skin on a flat surface with the grainedside up. The skin is then lightly brushed manually or by machine with a brush dipped in the sorbitol mixture. Immediately after the sorbitol treatment the skins are hung up to dry. Sometimes the tanner prefers to give the skins a light coating of neats-foot oil applied on the grain side of the skin following the sorbitol treatment and before drying.

Other ingredients may be added to the sorbitol solution, such as blood or egg albumen, milk,

' casein and dyes such as nigrosine, logwood extract V. Blood albumen 15% Nigrosine 1% Sorbitol syrup. I. Milk 10% Water 73 ,597,

It is, moreover, possible, after the leather has been dyed, by rubbing sorbitol in on the non-dyed side to give it the necessary degree of suppleness.

A gloss can then be developed by glazing and the final finishing for the particular use follows. While I have described the invention somewhat specifically for the purpose of establishing a clear disclosure so as to enable those skilled in the art to appreciate the value of this invention, it is understood that I am not to be limited to such e to, be understood that. solutions of these substances may be applied. Also instead of the pure substances I have used the technical products containing relatively small amounts of ash, sugar and other organic impurities, and the results ob tained with the technical products were equally as good as those obtained with the pure substances.

Having described my invention, what I claim i 1. A process of finishing leather which comprises treating the leather with a compound selected from the group consisting of the hygroscopic hexahydric alcohols and the water soluble, hygroscopic, anhydro derivatives of the hexahydric alcohols.

2. A process of finishing leather which comprises treating the leather with a hygroscopic hexahydric alcohol.

3. A process of finishing leather which comprises treating the leather with sorbitol.

4. A process of finishing leather which comprises treating the leather with idltol.

5. A process of finishing leather which comprises treating the leather with a water soluble.

hygroscopic, anhydro derivative or a hexahydric alcohol.

6. A process of finishing leather which comprises treating the leather with sorhitan.

7. A process of finishing leather which comprises treating the-leather with a mixture containing an oil and a compound selected fronr the group consisting of the hygroscopic hexahydric alcohols and the water'soluble, hygroscopic, anhydro derivatives of the hexahydric alcohols.

8. A process of finishing leather which comprises treating the leather with a mixture containing a hygroscopic hexahydric alcohol and an oil.

9. A process of finishing leather which comprises treating the leather with a mixture containing sorbitoland an oil;

10. A- process of finishing leather which comprises treating the leather with a mixture containing an oil, a. soap, and a compound selected from the group consisting of the hygroscopic hexahydric alcohols and the water soluble, hy-'-- groscopic, anhydro derivatives of the hexahydrie alcohols.

11. A process of finishing leather which comprises treating the leather with a mixture con- 12. A process 0! finishing leather which comprises treating the leather with a mixture containing sorbitol, an oil, and a soap.

13. In the process of finishing leather the step of fat liquoring which comprises treating the leather with sorbitol.

14. A i'at liquor bath for finishing leather, said bath containing sorbitol and an oil.

, 15. In the process of finishing of oiling oil which comprises treating the leather with sorbitol.

16. An article of manufacture comprising leather and a compound selected from the group consisting of the hygroscopic .hexahydric alcohols and the water soluble, hygroscopic, anhydro derivatives of, the hexahydric alcohols.

1'7. An article of manufacture comprising leather and a hygroscopic hexahydrlc alcohol.

leather the step 18. An article of manufacture comprisingleather and sorbitol.

19. An article of manufacture comprising leather and a water soluble, hygroscopic. anhydro derivative of a hexahydric alcohol.

20. An article of 'manufacture comprising leather and sorbitan.

JAMES '1. POWER.

taining a hygroscopic hexahydric alcohol, an

oil, and a soap. 

